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Rhythms of Life: Thyroid Hormone & the Origin of Species Paperback – March 1, 2006
I suggest that variations in patterns of thyroid hormone secretion (thyroid hormone rhythms) are key to both evolutionary change and human health. Thyroid hormone controls a huge variety of body characteristics and functions-including fetal growth, hair color, and the fight-or-flight response. Thyroid hormone has two essential jobs: controlling species-specific growth and keeping each individual body adapted to the conditions of light, temperature and food supply that vary with the seasons. My research suggests that thyroid metabolism also allows populations of individuals-species-to adapt to changing environmental conditions over evolutionary time. Moreover, since thyroid hormone is so critical to maintenance functions of the entire body, including the brain, this system also controls your day-to-day health.
My new theory provides such a revolutionary new perspective on our health that evolution suddenly becomes personal. Unravelling the conundrum of how wolves transformed into dogs becomes essential for explaining why each of our bodies function in slightly different ways as we grow and age, and why so many of us suffer from a host of increasingly common health problems, including depression, obesity, infertility, high cholesterol, hypothyroidism, and birth defects.
This is a truly testable scientific theory, peer-reviewed by well-respected evolutionary biologists. The concept is generating significant excitement within the scientific community because it takes Darwin's fundamental ideas to a whole new level. It not only provides the essential link between genes, individuals and the environment that's been missing from previous accounts, it has the power to transform modern medicine. Whether you're a dog-and-nature-lover or concerned with health issues, I guarantee this book will change the way you look at life.
- Print length274 pages
- LanguageEnglish
- PublisherTrafford Publishing
- Publication dateMarch 1, 2006
- ISBN-101412061245
- ISBN-13978-1412061247
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- Publisher : Trafford Publishing (March 1, 2006)
- Language : English
- Paperback : 274 pages
- ISBN-10 : 1412061245
- ISBN-13 : 978-1412061247
- Item Weight : 1.4 pounds
- Best Sellers Rank: #6,959,179 in Books (See Top 100 in Books)
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Jim C.
Yet after 76 pages of self-puffery about how innovative her hypothesis is, how revolutionary it is, going so far as to cite Kuhn, Crockford lets the cat out of the bag:
"In other words, I'm suggesting that the species-specific flow of thyroid hormone from the mother is largely what causes a chimpanzee fetus to grow into a chimpanzee rather than into a human, despite the fact that 99% of its genes are identical to ours. The newborn chimp produces thyroid hormone in its own chump-specific way and so continue to develop into a chimp and function like a chimp- perpetuating chimps that look and act virtually the same generation after generation."
She then proceeds to map out how her theory of pulsations of thyroid hormones being responsible for species differences could be tested, perhaps with exceedingly complicated sampling of the blood of wild animals, requiring new technology, etc. But the simplest test is already performed routinely. Do women with no endogenous thyroid function, taking oral (non-pulsatile) thyroxine, give birth to chimpanzees, or to non-human babies of any kind? Obviously the answer is no. Nothing could be farther from the case.
So the whole idea is fundamentally cracked. There is good evidence that the thyroid axis expresses one variation among many genetically-based variations that can contribute to alterations in development and temperament concomitant with speciation and domestication. But it can not account as strongly as Crockford's monomania would have it. Far from.
So this book interesting as a sort of object lesson in scientific crack-pottery, and specifically on the reluctance many observers have in believing that mutations alone can account for rapid and wide-ranging evolutionary change (as exhibited by the ID community as well). From that perspective, it is quite interesting. Crockford, however, needs to go back to the New Synthesis of Wright, Dobzhansky, et al. for review on population genetics, and to genetics in general to review the nature of heritability.
The most fascinating aspect of the book centers around Crockford's theories about the critical roles of thyroid hormones in evolution. As I began to read her theories I thought these theories are really out there, maybe "left field" or beyond. However, as I continued to read and tap into the background laid in her earlier chapters, my skepticism turned to, what if? Her theories if true could have significant implications in the field of evolutionary biology and medicine. The next logical step is to take the theories in this book and rigorously test them in a laboratory.
In summary, I enjoyed Rhythms of Life and learned many concepts that are of potential interest to both lay readers as well as experienced investigators. Crockford's novel and exciting theories on the roles of thyroid hormones in evolution may prove to be a major piece in the puzzle of evolution and human development.

